Test 3 -Skeletal Muscle Flashcards
Muscle
Little mouse
Muscle functions
- movement
- maintenance of posture
- join stabilization
- heat generation
movement of muscle
skeletal muscle attaches to the skeleton and moves the body by moving the bones
maintenance of posture
muscle function
certain skeletal muscles contract continuously to maintain posture, enabling the body to remain in standing or sitting position
join stabilization (muscle function)
muscle tone is a constant, low level of contractile force that is generated by a muscle even when it is not causing movement
muscle tone stabilizes joints by?
keeping tension on the muscle tendons that cross over joints just external to the join capsule
heat generation (muscle function)
muscle contractions produce heat that plays a vital role in maintaining normal body temperature at 98.6 F (37 C)
what are some special functional characteristics of muscle tissue that distinguish it from other tissues
contractility
excitability
extensibility
elasticity
contractability of muscles
- muscle cells shorten and generate a strong pulling force as they contract
- actin and myosin
excitability of muscles
nerve signals or other factors excite muscle cells, causing electrical impulses to travel along the cell’s plasma membrane, causing the cells to conract
extensibility of muscles
muscle tissue can be stretched by the contraction of an opposing muscle
elasticity of muscles
after being stretched, muscle tissue can recoil passively and resume its resting lenght
what are the three types of muscle tissue?
skeletal
cardiac
smooth
each type of muscle tissues can be characterized by what two main features?
- the presence or absence of striations in the muscle cells
2. whether control is voluntary or involuntary
striated vs nonstriated
- striated muscle tissue has stripes extending transversely across the muscle cells
- nonstriated muscle does not have the distinctive bands of striation
in muscles voluntary and involuntary refers to?
to the innervation of the muscle tissue
voluntary muscle
innervated by voluntary motor nerves and subject to conscious control
- you can control this muscle tissue at will
involuntary muscle
innervated by the involuntary portion of the nervous system and cannot be controlled consciously
skeletal muscle tissue
-located in the skeletal muscle, discrete organs that attach to and move
the skeleton
- make up 40% of the body weight
- cells are striated
- contractions is subject to voluntary control
cardiac muscle tissue
- occurs only in the walls of the heart
- cells are striated
- contractions is subject to involuntary control
- visceral muscle
smooth muscle tissue
- most found in the walls of hollow internal organs
- cells lack striations
- contractions is subject to involuntary control
- visceral muscle
what is an important similarities between skeletal and smooth muscles only
the cells of skeletal and smooth muscle tissu (only) are called fibers because they are elongated
in all three types of muscle tissue, muscle contractions depend on?
myofilaments
- specific types of microfilaments that are responsible for the shortening of muscle cells
the plasma membrane of muscle cells are called?
sarcolemma
the cytoplasm of muscle cells are called?
sarcoplasm
does the function of cytoplasm in comparison to sarcoplams or plasma membrane to sarcolemma differ?
no. they are the same, just different name
what holds the fibers of a skeletal muscles together?
several sheath of connective tissue
from external to internal:
- epimysium -> perimysium -> endomysium
epimysium
- “outside the muscle”
- an overcoat of dense, irregular C.T that surrounds the whole skeletal muscle
perimysium
- “around the muscle”
- a layer of fibrous C.T. that surrounds each fascicle
fascicle
a group of muscle fibers
endomysium
- “within the muscle”
- a fine sheath of C.T. consisting mostly of reticular fibers that surrounds each muscle fiber within each fascicle
What are the function of the fibrous connective tissue of skeletal muscles?
binds muscle fibers together and hold them in parallel alignment so they can work together to produce force
all three sheaths are continuous with?
with the tendon
tendon
the connective tissue structure that joins skeletal muscle to bones
what happens when muscle fibers contract?
they pull on the surrounding endomysium
Because of the continuity between sheath what happens after the surrounding endomysium is pulled?
the pull is then exerted on the perimysium, epimysium, and tendon
what else does the sheath provide?
provide a muscle with much of its elasticity and carry the blood vessels and nerves that serve the muscle fibers
in general, each skeletal muscle is supplied by?
one nerve, one artery, and one or more veins
where does the nerve, artery, and veins all enter or exit the muscle?
near the middle of its lenght
the nerves and vessels branch repeatedly where?
branch repeatedly in the intramuscular CT, with the smallest branches serving individual muscle fibers
capillaries of the skeletal muscle form a network within the
endomysium
the rich blood supply to muscles reflects the?
high demand that contracting muscle fibers have for nutrients and oxygen
the smallest nerve branches serve?
individual muscle fibers
what is neuromuscular joints?
interface between nerve and muscle fiber
synaptic cleft between neuron and muscle fibers
what is a muscle attachement
the location on a bone where a muscle connects to the bone
each skeletal muscle extends from?
one bone to another crossing at least one movable join
what happens when a muscle contracts?
it causes one of the bones to move while the other bone usually remains fixed
the attachment of the muscle on the less movable bone is called?
the origin of the muscle
the attachment on the more moveable bone is called?
(the muscle’s) Insertion
when muscle contracts what happens between insertion and origin?
muscles insertion is pulled towards its origin
in the muscle of the limbs, the origin is?
the more proximal attachment of the muscle
in the muscles of the limbs, the insertion is?
the more distal attachment
the origin and insertion of a given muscle can be at either attachment of the muscle, depending on?
a. what position of the body is in
b. the movement is produced as the muscle contracts
muscles attach to their origins and insertions via?
strong fibrous periosteum of the bone
what happens in direct or fleshy attachments
the attaching strands of the CT are so short that the muscle fascicles themselves appear to attach directly to the bone
in indirect attachments, the ct?
Connective tissues extends well beyond the end of the muscle fibers to form either a cordlike tendon or a flat sheet called aponeurosis
Which are more common attachments?
indirect attachments are more common than direct attachments and most muscles have tendons
raised bone markings are often present where?
where tendons meet bones (eg Greater trochanter)
microscopic anatomy of skeletal muscle fiber
skeletal muscle fibers are long, cyndrical cells
- diameter 10 - 100 um
- lenght: several cm (short muscles) to dozens of cm (long muscles
each skeletal muscle fiber is formed by?
the fusion of hundreds of embryonic cells.
- contains many nuclei
where are the nuclei located in skeletal muscle fibers?
they lie in the periphery of each fiber, just deep to the sacrolemma
the striations of skeletal muscle fibers are the result from?
from the internal structure of long, rod-shaped organelles called myofibrils
myofibrils
specialized contractile organelles unique to muscle tissue that make up more than 80% of the sacroplasm
- a long row of repeating segments called sarcomeres
sarcomeres
- “muscle segments”
- the basic unit of contraction
Z-discs or Z-lines
the boundaries at the two ends of each sarcomere are called?
where are actin filaments located?
attached to each Z-disc and extending towards the center of the sacromere
actin filaments
- (fine myofilaments) thin filaments which consist primarily of the protein actin
myosin filaments
cylindrical bundle of thick filaments that consists primarily of myosin molecules
where are myosin molecules located?
in the center of the sacromere and overlapping the inner ends of the thin filaments
myosin filaments also contains what enzyme?
ATPase enzymes that split ATP to release the energy required for muscle contractions
the sarcomere structrue explains?
the pattern of striations in skeletal muscle fibers
the dark bands are created by?
the full length of the thick filaments in the sarcomeres, along with the inner ends of the thin filaments
what region is dark bands in?
the A band
H zone
- central part of an A band,
- no thin filaments reach
M line
- in the center of the H-zone
- contains tiny rods that hold the thick filaments together
I bands
the two regions on either side of the A band, which contains only thin filaments
I bands forms which bands?
light bands
each skeletal muscle fiber contains two sets of?
two sets of tubules that participate in the regulation of muscle contraction
what are the two set of tubules in the skeletal muscle fiber
- sarcoplasmic reticulum (SR)
2. T tubules
Sarcoplasmic reticulum (SR)
an elaborate smooth endoplasmic reticulum whose interconnecting tubules surround each myofibril and run longitudinally along the myofibril
terminal cisternae
- “end sacs”
- larger perpendicular cross-channels over the junction between the A bands and I bands
The sacroplasmic reticulum stores ?
large quantities of calcium ions Ca2+
when are calcium ions released?
when the muscle is stimulated to contract
Ca2+ ions actions
- diffuse through the cytosol to the thin filaments, where they trigger the sliding filament mechanism of contraction
- after the contraction, the Ca@+ ions are pumped back into the SR for storage
muscular contraction in skeletal muscle is controlled by?
nerve generated impulses that travel along the sarcolemma of the muscle cell then these impulses are further conducted by T tubules
T tubules
deep invaginations of the sarcolemma that run between each pair of terminal cisternae of the sarcoplasmic reticulum
Because T tubules are continuations of the sarcolemma they conduct each impulse to?
they conduct each impulse to the deepest regions of the muscle fiber
Triad
T-tubules
the complext of a T tubule with flanked by two terminal cisternae at each A-I junction
the two types of muscle contraction involved in producing movements
- concentric contraction
2. eccentric contraction
concentric contraction
the shortens and does work
eccentric contraction
a muscle generates force as it lengthens
- essential for controlled movement and resistance to gravity
when muscles are acting “like a brake” they are contracting?
eccentrically
- landing from a jump
what explains concentric contractions of skeletal muscle?
sliding filament mechanism
sliding filament mechanism
- actin + myosin + cross bridges
- contraction results as the myosin heads of the thick filaments attach to the thin filaments at both ends of the sarcomere and pull the thin filaments toward the center of the sarcomere by swiveling inward
sliding filament mechanism
- what happens after a myosin head pivots at its hinges?
it lets go, returns to its original position, binds to the thin filament farther along its length and pivots again
the ratchet-like cycle of the sliding filament mechanism during a single contraction is?
repeated many times
- the thick and thin filaments do not shorten, they merely slide past one another
the sliding filament mechanism is initiated by ?
the release of Ca2+ ions from the SR and the binding of those ions to the thin filaments
Sliding filament mechanism is powered by?
ATP
what does the action of the thick filaments do?
pulls the two Z discs closer together, causing each sarcomere to shorten
a) causing the I bands to shorten
b) causing the H zones to disappear completely
Why does the A bands stay the same lenght?
because the length of the thick filaments does not change
the optimal resting length for skeletal muscle fibers is?
the lenght that will generate the greatest pulling force when the muscle is contracted
what is the optimal resting length?
i dont know
When does the optimal length occurs?
when a fiber is slightly stretched so that its thin and thick filaments overlap only to a moderate extent..Why?
skeletal muscles range of optimal operational lenght
runs from about 80% of their normal resting lenght to about 120% of that length
joins normal actions
do not let any bone move so widely that its attached muscles could not shorten or stretch beyond their optimal range
titin
a spring like molecule in sarcomeres that resists overstretching
where does the titin molecules in a sarcomere extend from?
from the Z disc to the thick filament and run within the thick filament to attach to the M line
caridac muscle
the muscle tissue of the heart wall
myocardium
thick layer formed by the cardiac muscle
contraction of the cardiac muscle does what
pump blood through the blood vessels of the circulatory system
cardiac muscle - discription
striated like skeletal muscle and it contracts through the sliding filament mechanism
what kind of cell are cardiac muscles?
single cells separated from one another by a delicate endomysium
- each cell contains one or two neuclei in its center, not at periphery
are cardiac muscle cells called fibers?
no
what is unique to cardiac muscle?
its cells branch and join together at complex junctions called intercalated discs so that they form cellular network
what are the three types of cell junctions that intercalated discs have?
desmosomes
fasciae adherans
gap junction
fasciae adherans
long, desmosome-like junctions
desmosomes and fasciae adherans function
hold the cells together
gap junction function
allow ions to pass between cells
where are most smooth muscle of the body found?
walls of viceral organs that contracts via the slliding filament mechanism
six major location of smooth muscle
- inside the eye
* ***in the walls of the - circulatory vessels
- respiratory vessels
- digestie tubes
- urinary organs
- reproductive organs
each smooth muscle fiber is a?
spindle shaped cell with one centrally located nucleus
- cells are separated by endomysium
- no s`triations or sarcomeres
what fills the sacroplasm of smooth muscle?
interdigitating thick and thin filaments
the fibers of smooth muscles in the walls of hollow viscera are?
grouped into sheets of smooth muscle tissue
- often two sheets are present, with their fibers oriented at right angles to each other
smooth muscle layers
- longitudinal layer
2. circular layer
circular layer and longitudinal layer of smooth muscle
- circular layer constricts the hollow organ
- longitudinal layer shortens the organ’s lenght
peristalsis
- around contraction
- a process by which the circular layer and longtitudinal muscle layers generate alternate waves of contraction and relaxation that propel substance through the organ
